Micro-pipetting of samples of fluid such as blood by use of small volume capillary tubes is a highly developed and advanced state of art. It is conventional in the known system to provide a shield for the pipette when it is not in use as a protective device. The shield is removably positioned on the pipette assembly so that it can be removed from the pipette when the pipette is introduced to the sample producing source for pipetting activity. Throughout the years, the shield has been used for various other purposes. For example, the shield is often used as a puncturing device since it has a closed protective end and forms a cap for the pipette. The closed end can be used to puncture diaphragms on reservoirs containing diluents and other types of medicaments to be used with the sample collected in the pipette.
It should also be kept in mind that with present day technology the entire pipetting system including the shields are manufactured of low cost disposable materials which are mass produced in large numbers. In view of the cost factor, it is naturally important to maintain as low a cost as possible from a manufacturing and use standpoint.
Naturally, automation has significantly reduced costs for mass produced items and pipette assemblies fall within this general category. Thus, the pipette assembly including the shields are independently automatically mass produced and assembled prior to use. During this procedure, it is not unusual for the shields to stack or nest one within the other as part of an automated system or even a manual system prior to assembling the shields to individual receiving pipettes in their protective capacity. With conventional type of pipettes shields presently in use, nesting of the shields often results in frictional interengagement or locking of the shields together which makes their disassembly more difficult when they are individually introduced to a receiving pipette. It is envisioned that a cost reduction can be provided if the shields could be nested in a manner which facilitates their ease of removal from one another for assembly with the remainder of the pipetting assembly.
Furthermore, an improved shield structure which facilitates its use as a puncturing device naturally also would be desirable in the art. Particularly, it would be helpful if the puncturing device could contain control means thereon to facilitate limitation of the penetration of the device after it has accomplished the initial puncturing action. This naturally provides a guard against contamination of the end of the shield which would occur if the shield contacts the contents of the reservoir.
Micro-pipettes with protective shields are known in many diverse fields. One particular area of common use is in the medical field where small samples of fluid such as precise micro-quantities of blood are collected and tested. Naturally other pipetting fields also require the use of a protective shield to guard the pipette when it is not being used. An example of a prior art patent in this area relating to general pipetting procedure and where a protective shield is employed is Roach U.S. Pat. No. 3,494,201 issued on Feb. 10, 1970. In contrast, examples of the type of pipette assembly under consideration which pertain to the medical profession are disclosed in U.S. Pat. Nos. 2,965,255 to Gerarde on Dec. 20, 1960; 3,433,712 to Gerarde on Mar. 18, 1969; 3,518,804 to Gerarde on July 7, 1970; and 3,779,083 to Ayres et al on Dec. 18, 1973. These references disclose the general pipetting concept and various types of known protective shields used with the pipette.